The Ethereal Border existed adjacent to the Material Realm and connected it to all other Inner Planes. When travelers crossed into the Ethereal, they and all their possessions were converted to their Ethereal equivalents: metal became ethereal metal, flesh became ethereal flesh, and so on. This allowed movement in any direction through the solid matter of the adjacent plane, and there was a sense of "up" and "down", though no real gravity existed.
Creatures on the Ethereal Plane could see into the Prime Material, but could not affect the energies of the plane. However, certain creatures dwelled primarily on the Ethereal Plane and could shift between it and the Material Plane virtually at will. Examples of these included Ghosts and Phase Spiders.
The Ethereal was considered to be a transitive plane according to the Cosmic Wheel cosmology, a connector to other planes.